This invention relates to a power supply for a television receiver.
Various power supply circuits have been utilized in television receivers. One such power supply circuit utilizes a rectifier adapted to be coupled to a source of alternating current voltage to produce a pulsating direct current voltage. A choke input filter coupled to the rectifier provides a direct current voltage having a suitable ripple factor required by a circuit which is used in the production of, for example, high voltage required at the ultor electrode of the kinescope tube.
In certain applications, the choke input filter is preferred over a capacitance input filter for the following reasons: (1) a low ripple factor direct current voltage having a magnitude less than the peak voltage of the source of alternating current potential is developed without a power transformer and without high power dissipation, (2) direct current voltage remains relatively constant throughout a predetermined range of load current, and (3) direct current voltage is virtually independent of filter capacitance values.
The choke input filter, however, has one disadvantage. That is, if the choke inductance is reduced by shorted turns or the choke being externally shorted resulting in an increase in the direct current voltage produced at the output of the choke input filter, thereby increasing the high voltage to the kinescope without rendering kinescope unviewable, there is a possibility of exposure of the viewer to X-ray radiation in excess of 0.5 mR/hr (HEW prescribed isoexposure limit). If, however, the kinescope is rendered unviewable when the choke inductance decreases below a predetermined level, the viewer will be encouraged not to continue to operate the television receiver, thereby protecting him from the increased X-ray radiation.